Conventional loudspeakers typically include a frame, a magnetic circuit having a magnetic gap, a voice coil, a diaphragm, and a center pole. The magnetic circuit includes a yoke, a ring magnet, an annular top plate, and magnetic fluid. The center pole is a columnar projection extending from the center of the yoke.
The magnetic circuit is stored in and coupled to the frame. The outer periphery of the diaphragm is coupled to the frame. The magnet is coupled to the yoke. The top plate is coupled onto the magnet. The center pole penetrates the centers of the magnet and the top plate. The magnetic gap is located between the side surface of the center pole and the inner circumferential surface of the top plate. One end of the voice coil is coupled to the diaphragm and the other end is inserted in the magnetic gap.
In the above configuration, the magnetic fluid is injected between the voice coil and the center pole and also between the voice coil and the top plate.
One example of techniques related to the present application is Patent Literature 1.